In recent years much attention has been directed toward the development of new sources of protein for human consumption. There exists a need for protein material which can be incorporated in foods or which is usable as a basic proteinaceous substance for human consumption.
One possible solution to the problem of supplying the ever increasing world-wide need for food protein is provided by processes for the bio-synthetic manufacture of protein through the growth of microorganisms on various substrates. It is known, for example, that microorganisms such as bacteria and yeast, which are grown by single-cell reproduction, contain high proportions of proteins and can be utilized directly in foods or can be treated to recover protein isolate.
In order for single-cell proteins to compete with vegetable proteins and to share the protein market, it is necessary that it be processed to remove nucleic acid, primarily ribonucleic acid (RNA).
The human metabolic system produces uric acid as the result of the metabolism of materials such as ribonucleic acid. Since man does not have a uricase enzyme system, uric acid is not broken down and excreted with urine. However, if produced in larger quantities than the body can excrete, the body stores uric acid leading to the condition known as gout.
In 1972 the Recommended Daily Allowance of The Food and Nutrition Board, National Research Counsil in protein was 65 grams per day for a 70 kilogram adult male. The Protein Advisory Group of the United Nations System recommended that the amount of nucleic acid ingested per day from microbial protein should be less than 2 grams. Therefore, the nucleic acid content of the protein should be less than 6%, if microbial protein supplied 50% of dietary protein. The nucleic acid content should be below about 3%, if microbial protein is the sole source of protein in the diet.
Various methods have been proposed to reduce nucleic acid in microbial derived protein.
U.S. Pat. No. 4,066,827 describes a polyion complex having a nucleic acid base, which is disclosed as useful in the separation and purification of proteins.
U.S. Pat. No. 3,885,050 describes treating protein containing microbial cells with aqueous alcoholic solutions to remove undesirable flavor and odor substances.
U.S. Pat. No. 3,937,693 describes reducing the nucleic acid content of microbial protein by the use of an alcohol, coupled with pH and temperature control.
U.S. Pat. No. 3,960,659 describes reducing the nucleic acid content by the use of extra-cellular ribonuclease.
U.S. Pat. No. 3,867,555 describes the use of alkali to reduce nucleic acid in microbial protein.
U.S. Pat. No. 4,041,189 teaches the reduction of nucleic acid content in certain Fungi Imperfecti by controlling pH and temperature.
U.S. Pat. No. 3,887,431 describes a process for reducing nucleic acid in microbial protein products involving utilization of endogenous nuclease.
U.S. Pat. No. 3,903,314 describes several methods for reducing nucleic acid content of microbial proteins.